Developing neuroprotective strategies for proteinopathy. The lesions seen in the degenerating neurons of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin positive inclusions (FTLD-U) consist primarily of abnormal TDP-43 protein. Pathological TDP-43 containing deposits associated with motor neuron neurodegeneration are the hallmark pathology in over 90% of ALS cases, including both familial and sporadic types. How aggregated, ubiquitinated and phosphorylated TDP-43 protein causes neuronal dysfunction and neurodegeneration remains incompletely understood. This work focuses on extending previous studies to complete the molecular dissection of the mechanisms causing neurodegeneration in ALS and FTLD. In the previous funding period we characterized a C. elegans model of ALS mutation driven TDP-43 proteinopathy and investigated the molecular, cellular, and genomic basis of TDP-43 neurotoxicity. We identified phosphorylation of TDP-43 at serines 409/410 as a critical molecular species driving neurotoxicity, and identified kinases modulating neurodegeneration by controlling the accumulation of phosphorylated TDP-43. The specific aims of this competitive renewal are: 1) Determine the relative toxicity of phosphorylated wild type TDP-43 and the role of kinase activation in the genesis of phosphorylated TDP-43; 2) Identify the cellular machinery responsible for detoxifying phosphorylated TDP-43 3) Dissect the mechanisms by which Ubiquilin mediates TDP-43 neuropathology and neurodegeneration. The development of neuroprotective strategies for TDP-43 related neuropathology in ALS and FTLD is the long term objective of this work. By completing the proposed experiments we will construct additional models of sporadic ALS/FTLD, address the critical question of whether or not pS409/410 TDP-43 is a neurotoxic species in mammals, dissect the molecular mechanism mediating TDP-43 toxicity and capitalize on this information to develop new translationally relevant neuroprotective strategies for targeting TDP-43 neurotoxicity.